The present invention relates to an electric pump, and more particularly, to an electric pump formed integrally with an electric motor.
An electric pump of this kind is known from, e.g., Jpn. Pat. Appln. KOKAI Publication No. 52-79302. In the conventional electric pump described in this publication, a stator assembly of a motor is water-tightly held in a casing having a circular cross section, and a double center shaft supporting a rotor assembly for the motor and an impeller for a pump is disposed inside of the stator assembly in a center hole of the casing. The double center shaft includes an outer cylindrical portion and an inner solid shaft portion. The rotor assembly corresponding to the stator assembly in its radial direction is fixed to an outer peripheral surface of the outer cylindrical portion, and opposite ends of the inner solid shaft portion are projected from opposite ends of the stator assembly in its longitudinal direction. The opposite ends of the inner solid shaft portion are rotatably supported by a pair of bearings supported in the center hole of the casing. The impeller for the pump is fixed to one of the ends of the inner solid shaft portion between one of the bearings supporting said one end of the inner solid shaft portion and one of the ends of the stator assembly corresponding to said one end of the inner solid shaft portion. One end of the outer cylindrical portion corresponding to said one end of the inner solid shaft portion is enlarged in its radial direction along the impeller between the impeller and said one end of the stator assembly facing the impeller. The other end of the outer cylindrical portion is fixed to the other end of the inner solid shaft portion, and has a plurality of through-holes passing through the outer cylindrical portion from its outer peripheral surface to its inner peripheral surface.
In the conventional electric pump constituted as described above, a fluid is introduced into the center hole of the casing from a side of the other end of the double center shaft, and is further introduced, through the plurality of through-holes in the other end of the outer cylindrical portion of the double center shaft, into the center hole of the outer cylindrical portion. The fluid in the center hole of the outer cylindrical portion is guided to the impeller along the inner solid shaft portion, and then, is thrown out radially outwardly between the impeller and said one end of the outer cylindrical portion by the impeller. The fluid thrown out from the impeller collides against the inner peripheral surface of the casing, and then, is discharged into outside of the center hole of the casing from a side of said one end of the double center shaft.
The conventional electric pump constituted as described above has the following drawbacks: That is, since the impeller for the pump and the combination of the rotor assembly and the stator assembly for the motor are disposed adjacent in the longitudinal direction of the double center shaft, a size of the conventional electric pump in the longitudinal direction is increased; The double center shaft has a large size in its radial direction, and increases the size of the conventional electric pump in its radial direction; And, the double center shaft of a complicated structure which is independently formed and independently assembled, a combination of the rotor assembly and the stator assembly for the motor which are independently formed and independently assembled, and the impeller for the pump which is independently formed and independently assembled, all complicate the manufacture and the assembly of the conventional electric pump, and increases the manufacturing costs thereof.
The present invention is derived from the above circumstances, and an object of this invention is to provide a new electric pump which can decrease sizes in its longitudinal and radial directions of the rotor assembly, and which is simple in its structure and can easily be manufactured and assembled so that its manufacturing cost can be lowered.